PDGF is a ubiquitous growth factor responsible for cell proliferation and directed cell movement. It has been implicated in embryogenesis and normal development as well as in abnormal proliferation of cells that occurs in diseases such as atherosclerosis, neoplasia and pulmonary fibrosis. In addition to being a strong mitogen, PDGF has been described to be a powerful vasoconstrictor and hence may play a key role in both structural remodeling of the vasculature as well as in the control of vascular smooth muscle tone. The proposed studies on the regulation of PDGF production by endothelial cells aim to address molecular mechanisms underlying such very important clinical problems as atherosclerosis and pulmonary hypertension. bFGF down-regulates PDGF B-chain mRNA levels resulting in decreased protein secreted. In addition, preliminary studies indicate that hypoxia, a strong inducer of vasoconstriction significantly increases PDGF B-chain mRNA levels. Proposed studies will address how bFGF and hypoxia regulate the PDGF B-chain gene transcriptional rate and/or the stability of its mRNA. Functional assays in tissue culture cells using in vitro generated deletion mutants of the 5' end of PDGF-B gene promoter will locate and identify cis-acting regulatory elements. The effect of other growth factors and cytokines such as alpha FGF, TGF beta, and interferon-beta2, will be studied since they are known to modulate perivascular events via controlling the proliferative state of the fibroblasts and smooth muscle cells underlying the endothelium. The studies will be further extended to primary cultures of pulmonary microvascular endothelial cells and in vivo experiments examining PDGF-A/B mRNA levels in situ in the lung in order to further characterize the role of PDGF in pulmonary hypertension.